Inkjet pens generally comprise a carrier that supports a print head comprising a silicon die containing a plurality of nozzles for ejecting ink. For example, a single die may have as many as 1200 nozzles each individually controlled using circuitry on board the die. The circuitry receives data from an external controller over interconnect wires which may comprise wire bonding, tape automated bonding (TAB) or other known conventional interconnect technology.
The interconnect wires are generally protected against contacting the ink using an encapsulating material. However, the encapsulating material may be subject to degradation resulting from contact with the corrosive inks that are handled by the inkjet pen. When the encapsulation material is attacked by the ink, it may expose the interconnection wires which then become shorted or corroded themselves.
FIG. 1 shows an exemplary inkjet pen 10 according to the prior art. Inkjet pen 10 is a wide-area inkjet pen having a plurality of print heads 20 arranged in a staggered relationship to cover a larger area of the print media with each pass. Each print head 20 comprises a silicon substrate with a plurality of nozzles 22 formed therein. The print heads 20 are wire bonded to flexible printed circuit board 14, which bends over a corner of carrier 12. Electrical contacts 18 are provided on a second surface of carrier 12 well away from print heads 20 to prevent contact with ink, which could short circuit the connections. Electrical contacts 18 are used to provide electronic communication between print heads 20 and an external controller circuit (not shown). Ink is provided via port 21 from an ink supply (not shown). The ink passes through a manifold 16 and enters each print head 20 from underneath.
FIG. 2 shows a cross section view of inkjet pen 30 having a single print head 20. The single print head will typically be responsible for printing a single color ink, so that for the typical four-color system having cyan, yellow, magenta, and black (CYMK) inks, four print heads will be provided, typically arranged adjacent one another. Print head 20 includes wire bond sites at either end to provide signal communication over wire bonds 24. Wire bonds 24 are encapsulated by encapsulating material 26. The bonds provide a connection between print head 20 and ceramic substrate 14 so that print head 20 can receive print data. Ceramic substrate may be any ceramic material with electrical traces provided thereon. Alternatively, a rigid circuit board may be used. The print data is interpreted using processor circuitry in print head 20 to generate signals for firing each nozzle at appropriate times to eject a droplet of ink onto a print media such as a sheet of paper. The use of processor circuitry allows for a reduction in the number of wire bonds needed to supply the necessary data for the large number of nozzles on board print head 20. For example, a print head having 1200 nozzles may require tens of connections to supply it with necessary data and power to operate.
Because the electrical connections are so close to the print nozzles, the encapsulating material comes into contact with ink which attacks the material. As print resolution increases, and as technology advances in print head design resulting in increased printing speed, more and faster electrical connections have become necessary to handle increased data throughput. Increased wire bond connections result in lower yields in production. Furthermore, as the number of interconnects increases, the likelihood that one or several interconnections will become shorted by the ink and/or corroded beyond use increases, which reduces the expected life of the pen. This problem is exacerbated by the advent of more aggressive inks, which are provided to improve clarity on a variety of media.
In light of the above, it would be desirable to provide some interconnect technology that provides reliable high speed electronic communication to a ink jet pen which is less vulnerable to corrosion and shorting than the currently available technologies.